Recuperator



F. l. TONE.

RECUPERATOR.

APPucATmN FILED MAR. 24, 1922.

INVENTOR types of recuperators.

lli'lRiiA il'. TONE, 0F' GA JFS, NEW TURF, ASSIGNGR T0 THE CARBORUNDUM BUMP, OF NG le FALLS, hl YORK, A COEJPURATION UF IIPENNSYLVAN IA.

ECUPIERATOR.

Application med March 2t, 1922.

To all/whom t may concern:

Beit known that ll, FRANK citizen of the lUnited States, residing at NiagaraFallS, in the county of Niagara and State of New York, have invented a new and useful llmprovement in Recuperators, of which the following is a full, clear, and exact description.

This invention relates to refractory structures known 'as recuperators which are used for preheating air or gas in the operation of many types of heating and combustion Vfurnaces, and particularly refers to the use of silicon carbide in the construction of certain parts of the recuperators by the use of which much more ecient results are obtained than with the constructions heretofore used.

' A recuperator is a device in which the waste heat of escaping gases is given out to.

colder air or gas by a transfer ofthe heat through the walls of the passages which separate the respective streams of gases.

Tn the drawings, in which is illustrated the preferred embodiment of the invention,- F

Figure l is aA horizontal section taken along the line ll-T of Figure 2; and

Figure 2 is a vertical section taken along the line lll- TT of Figure 1.

Tn the drawings, the invention is illustrated as applied to one of the common The highly heated v gas which is brought to the recuperator for the purpose of extracting its sensible heat is shown as entering the recuperator at 1. llt traverses three banks of tubes 2, 3 and 4L set in a straight line longitudinally and is then discharged from the recuperator at 5. lRecuperator parts, especially the wallsl or partitions separating the hot and cold gases, are usually made of fire clay, but this material while able to stand fairly high temperatures is not a good conductor of heat: Tron is sometimes used but this does not stand 4very high temperatures.

Tn my construction the tubes are refracf tory forms composed of silicon carbide grains bound together with a refractory binder after the manner of fire brick and are made with the thinnest possible walls which will still meet the mechanical stresses of the tubes and enable them to hold their shape at the temperatures reached. The cold gases which are passed through the recuperator J. TONE, aV

Serial No. 546,283.

for the purpose of absorbing'heat from the hot gases are shown as entering the recuperator at 6, and pass through the passes formed by the banks numbered 4, 3 and 2, successivel around the outside of the tubes absorbing eat by conduction and radiation.

My invention relates to the use of silicon carbide as a refractory heat conducting and heat emitting medium in the recuperator and when used in the proper form it greatly increases the capacity of the recupera-tor and the fuel economy of the furnace. ll have discovered that certain properties of silicon carbide function together in a way to give most ecient results when used for this purpose. These properties are r'1st, heat emissivity, 2nd, thermal conductivity, 3rd, low co-etlicient of expansion, and llfth, tra-ns' verse strength.

The emissivity factor of a substance is the measure of its capacity to take up heat at the surface where it comes in contact with the substance carrying the heat, and likewise the factor which represents its capacity to similarly give up this heat at its surface to a colder medium, the factors being the same in each case. The emissivity factor of silicon carbide at 1000.o C. is 0.1() gram calories per square centimeter per second or about two times greater than that of'rc brick. This means that when silicon carbide is in contact with hotter gases. it will, other things being equal, take up the heat from the gases two times faster than fire clay, and likewise will emit the heat to colder gases at the same relative rate. lt is apparent that this factor is of prime importance in a regenerator material.

The second property of silicon carbide which its it for recuperators is its thermal conductivity. llts thermal conductivity is about five times that of fire clay refractories. The faster the heat is conducted through the recuperator walls, the more heat will be absorbed at the surface bythe colder gases, and the reverse is also true that the more rapidly the heat is conducted from the hot surface of the wall to the cold surface, the more rapidly will the heat be emitted at the cold surface, other factors being equal. This factor therefore plays an important part in the walls of the recuperators.

The third property of silicon carbide which is of special value in recuperators is 4which fits it for recuperator construction is its high mechanicall strength'. Silicon carbide when made into refractory forms by Well known processes, such as the bonding of the silicon carbide grains'with a Vitrified clay binder afterthe manner'iof. fire@ brick, has a remarkable mechanical strength not only at normal temperatures but at the higher ranges of temperature reached in the recuperator. For example, at 13502 C., ,it

has a modulus of rupture of approximately 2200 pounds per square inch. The modulus of rupture of fire clay refractories at 1350O C. is approximately 115 pounds per square inch, that is to say at recuperator temperatures a4 silicon carbide refractory has about nineteen times: the cross-breaking strength of a lire clay refractory. F or this reason silicon carbide refractory forms can be applied in many locations with very great advantage particularly Where the form has to sustain itself when extended over a long span and supported only at the ends.`

The term silicon carbide as used herein is intended as a term of general definition and not of limitation, and to include refractoriesf containing silicon carbide on admixture with other materials, such, for example, as bonding materials.

I have shown in the drawings and have described a particular form of recuperator to which my invention is applied, but this is only one of a number of forms in which it may be used. The recuperator may be in the form of passages with plane partitions or septa forming the Walls of the parallel t passages, the alternate passages being used for the hot and cold gases. It is also possible to apply the principle to concentric rings or tubes.

The present invention is therefore not limited to its illustrated embodiment, but may be otherwise embodied within the scope of the following claims.

I claim:

1. A recuperator having silicon carbide heat transferring Walls, substantially as described.

2. A recuperator having a plurality of passages provided with heat transferring silicon carbide walls, substantially as described.

In testimony whereof I have hereunto set my hand.

FRANK J. TONE. 

